It's a day to honor the national flag which is also known as Maple Leaf or l'Unifolié (French: "the one-leafed"). On this day in 1965, the Canadian flag was first raised over the Parliament Hill in Ottawa.
The National Flag of Canada is a red flag with a white square in its centre, which features a 11-pointed red maple leaf. This flag symbolizes freedom, peace, respect, and justice.
The day is marked by flying the flag, occasional public ceremonies, and educational programs in schools. It is not a public holiday, although there has been discussion about creating one.